The invention relates to a device and a system for carrying out search procedures in a mobile radio receiver.
In order to produce and maintain a radio connection between a mobile radio receiver (mobile station) and a transmitter (base station), the mobile radio receiver must be synchronized to the transmitting base station. In addition to frequency synchronization, which is not considered any further in the following text, frame and time slot synchronization of the receiver must also be carried out with a frame and time slot structure of the received radio signal, as predetermined by the transmitter.
For frame and time slot synchronization, the base station transmits specific, standardized data sequences. These data sequences are detected in the mobile station by carrying out suitable search procedures. The frame and time slot synchronization of the mobile station is then carried out based on the detection times of the data sequences.
Radio signals in cellular mobile radio systems are subject to multipath propagation. This means that a radio signal that is transmitted from the base station reaches the mobile station as a multi-component signal with different delay times relating to the individual signal paths. A delay estimation is required in order to determine the different signal delay times of the signal components. Likewise, the delay estimation for the individual signal components can be carried out by a search procedure in the mobile station.
Devices for carrying out such search procedures are referred to in mobile radio technology as xe2x80x9csearchersxe2x80x9d (search circuits). It is already known for search circuits to be provided in the form of filters that are matched to the signal (matched filters). The large area required and current drawn by a circuit such as this, as well as its lack of flexibility in terms of possible variations of the search procedure, are disadvantageous.
It is accordingly an object of the invention to provide a device and a system for carrying out search procedures in a mobile radio receiver that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and whose circuitry construction is simple (so that it thus also occupies a small area and draws little current) while, at the same time, has high flexibility for carrying out different search procedures.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for carrying out search procedures in a mobile radio receiver. The device includes a random access memory, a read only memory, and a correlation device. The random access memory is for storing a digital received data sequence including individual sequence elements of predetermined length N obtained from a received radio signal. The read only memory stores a predetermined, digital correlation data sequence including sequence elements each having a respective length. The correlation device has two sections for correlating the digital received data sequence with the predetermined, digital correlation data sequence. A first of the two sections correlates the individual sequence elements of predetermined length N in the received data sequence with the individual sequence elements of the same length in the correlation data sequence during parallel data processing in each case, and produces a sequence element correlation result for each correlation. A second of the two sections sums a variable number K of the sequence element correlation results to form an accumulated correlation result during serial data processing.
With the objects of the invention in view, there is also provided a system including two devices as described in the previous paragraph and a fourth section shared by both devices. The common fourth section is in the form of an adder for adding the accumulated correlation results calculated in the second sections of the first and second devices.
One major aspect of the invention is that the correlator device is formed from two components (first section and second section), with the first section having a parallel structure and the second section having a serial structure. The first section is used to produce sequence element correlation results relating to the sequence elements quickly and with little effort, using parallel data processing. These sequence element correlation results can be interpreted as xe2x80x9cintermediate resultsxe2x80x9d of the overall correlation task. In the second, serial section, a variable number K of sequence element correlation results (that is to say intermediate results) are used for calculating the accumulated correlation result. The capability to vary the number K allows the device to be used for carrying out quite different search procedures (in particular for frame and time slot synchronization and for delay time estimation), and it is possible to use correlation data sequences with different lengths, and to take account of different accuracy requirements with regard to the accumulated correlation result. Furthermore, the design concept according to the invention also makes it possible to provide a search circuit that is extremely advantageous in terms of the area required and the current drawn.
The first section preferably contains a number of memory banks (specifically P), each having N memory cells, where P is the oversampling factor that is used to obtain the received data sequence from the received radio signal. Thus, in the case of double oversampling, the first section contains two memory banks. This design allows the alternating storage of the sample values in the two memory banks, and thus allows the calculation of the sequence element correlation results with regard to xe2x80x9cearlierxe2x80x9d and xe2x80x9claterxe2x80x9d sample values of the elements of the digital received data sequence by appropriate selection of the first or of the second memory bank, respectively.
The correlation of the sequence elements (of length N) of the digital received data sequence with corresponding sequence elements of the same length in the correlation data sequence is preferably carried out by a multiplication data processing stage, which is provided in the first section and includes N multipliers connected in parallel.
One preferred refinement of the invention is distinguished in that the number K of sequence element correlation results that can be added up in the second section is varied by a control device as a function of the search procedure to be carried out, and/or as a function of the length of the digital received data sequence, and/or as a function of the desired calculation accuracy with regard to the accumulated correlation result.
The device according to the invention can be disposed in the quadrature (Q) branch or in the in-phase (I) branch of the mobile radio receiver. One preferred embodiment of the invention is formed by a system which has two devices according to the invention, in each case one for the Q branch and the other for the I branch of the received radio signal, and which furthermore contains an adder for addition of the accumulated correlation results (which may subsequently also be squared) produced by the two devices. In this way, the accuracy of the correlation result calculated by the system can be increased further (in comparison to the accuracies of the correlation results for the I and Q branches calculated independently of one another).
In the system according to the invention, the xe2x80x9cthird sectionxe2x80x9d is equivalent to the xe2x80x9cthird sectionxe2x80x9d of the device. Likewise, in the system, the xe2x80x9cfourth sectionxe2x80x9d is equivalent to the xe2x80x9cthird sectionxe2x80x9d of the device.
Further advantageous refinements of the device according to the invention are specified in the dependent claims.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and a system for carrying out search procedures in a mobile radio receiver, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.